[XviD-devel] Coefficient thresholding

[Radoslaw 'sysKin' Czyz]

> However I have one trailer which I constantly use for
> checking different motion estimations with fixed quant 3 and MPEG
> quantization. So I tested it with coeff thresholding enabled and there
> IS a drop in filesize compared to older builds - about 600 kb. To get
> to the point, after watching this trailer I noticed that too much
> details were removed, which was the most noticable on human faces.

I have to admit - I didn't really check any video with this. However,
it's quite obvious that not coding some coefficients will result in
smaller filesize *and* worse quality. The problem is, if in fixed
filesize/bitrate the general quality is better or worse.
I trusted PSNR on this. I didn't check myself.

It's very good that coeff thresholding is a flag, because - now when
I think of it - it really removes some details, while savings in
bitrate should remove some blocks. A step in a direction of h.263
quant type.

> It looks like TOOSMALL_LIMIT is set too high (or is that too low?).

If I remember correctly, TOOSMALL_LIMIT of 2 gave me a reasonable PSNR
improvement, too. It was something like 0.07 (compared to 0.10 for 3).

I don't know if it's too late, but I recommend not to make coeff
thresholding a flag but an integer of 1, 2, or 3. Users could choose
what they like. (oh great now I remember the discussion how users get
confused when they have too many options available......)

Thanks for your mail, Milos.

Radek